1. Field of the Invention
The present invention relates to a charging apparatus, a secondary battery apparatus, a charging system, and a charging method that allow a signal to be exchanged between the charging apparatus and the secondary battery apparatus.
2. Description of the Related Art
In recent years, a secondary battery for a power supply has been used for a portable electronic unit such as a portable telephone unit or a VCR that is equipped with a camera. When such a portable electronic unit is used, the secondary battery thereof should be charged. When the secondary battery is charged by a charging apparatus, the battery voltage and charging current are detected so as to determine whether the secondary battery is fully charged by the charging apparatus.
Depending on the characteristics of a secondary battery, the temperature thereof should be detected in addition to the battery voltage and charging current. The secondary battery has a chargeable temperature range. When the secondary battery is charged out of the chargeable temperature range, the characteristics thereof deteriorate. To prevent such a situation, such a secondary battery has a temperature detecting sensor. The charging apparatus can obtain the detected result of the temperature detecting sensor.
The chargeable temperature range of a secondary battery is different from the dischargeable temperature range thereof. For example, as shown in FIG. 1, the chargeable temperature range T1 of a lithium-ion battery is from around -10.degree. C. to around 60.degree. C., whereas the dischargeable temperature range T2 thereof is from around -20.degree. C. to around 90.degree. C. When a secondary battery is charged out of the chargeable temperature range T1 or discharged out of the dischargeable temperature range T2, the characteristics thereof deteriorate.
FIG. 2 is a block diagram showing the structure of a charging system having a charging portion and a secondary battery portion. The charging portion and the secondary battery portion are connected so as to exchange a signal. The secondary battery portion is hereinafter referred to as battery pack. In FIG. 2, the charging portion is composed of a PNP type transistor 221, a controlling circuit 222, and a receiving circuit 225. The battery pack is composed of a detecting circuit 223 and a signal circuit 224. A DC power is supplied from input terminals IN-AS and IN-BS. The input terminal IN-AS is connected to the emitter of the transistor 221. The collector of the transistor 221 is connected to the output terminal OUT-A. The base of the transistor 221 is connected to the controlling circuit 222. The controlling circuit 222 is connected to a terminal TM-B. The receiving circuit 225 is connected to a terminal TM-A. The receiving circuit 225 receives a signal from the signal circuit 224 of the battery pack. The receiving circuit 25 controls the controlling circuit 222 corresponding to the signal received from the signal circuit 224. When the receiving circuit 225 receives from the signal circuit 224 a signal that represents that the secondary battery has stopped charging, the receiving circuit 225 causes for example a displaying means to inform the user of such a situation. The input terminal IN-BS is connected to an output terminal OUT-B.
The output terminal OUT-A of the charging portion and an input terminal IN-AP of the battery pack are connected. The output terminal OUT-B of the charging portion and an input terminal IN-BP of the battery pack are connected. The terminal TM-A of the charging portion and a terminal TM-C of the battery pack are connected. The terminal TM-B of the charging portion and a terminal TM-D of the battery pack are connected. The detecting circuit 223 is disposed between the terminal TM-D and the input terminal IN-BP. The terminal TM-C is connected to the signal circuit 224. The signal circuit 224 supplies to the charging portion a signal that represents the current state of the battery pack (for example, the temperature of the battery pack exceeds the chargeable temperature range and thereby the battery pack has stopped charging the secondary battery). The input terminal IN-AP is connected to an output terminal OUT-AP. The input terminal IN-BP is connected to an output terminal OUT-BP. The output terminals OUT-AP and OUT-BP are connected to the secondary battery.
Thus, in the conventional charging system, since many signal lines and signal terminals are required to supply a signal, the size of the battery pack becomes large and thereby the cost thereof rises.